Electrodeposition

Electrodeposition of metal inside the nanopores of a membrane is generally performed in baths containing metal salts. The baths are either acidic or basic and use 

One of the earliest studies of Au nanowire (diameter 8 nm) fabricated by electrodeposition in a 5 pm thick etched track mica was reported in 1986 [26]. Effect of weak-localization and electron-electron interaction was studied down to 0.3 K. However, in the last decade especially in the last 5 years the field of electro-deposited nanowires in templates has been intensively investigated [27]. The application of such metallic nanowires in magnetism has been reviewed [28]. 

An ordered array of ZnO nanowires on alumina membranes was prepared by oxidizing electrodeposited Zn nanowires in air at 300 °C. The electrodeposition was carried out from an acidic bath of ZnS04-7H20 (0.3 M Boric acid and 0.28 M ZnS04-7H20). The grown nanowires showed PL at 55 nm. 

10 nm CdS Q-dots have been deposited in alumina membranes [41] by electrolyzing the membrane with H2SO4 and then dipping it in boiling CdS04. The acid treatments leave S ions on the templates. The Cd + ions react with the S ions to form CdS in the nanopores. The array of Q-dots shows Raman lines that are red 

The electrodeposition method is among the highly efficient techniques that have been used for the formation of various nanocrystalline and nanostructured materials such as thin nanofilms, nanorods, nanowires, and nanosheets. It has been successfully achieved by the deposition of metal or metal alloys on an electrode surface. The process is called electroplating. Electroplating of electrode surfaces is based on the method of electrodeposition [41]. It involves the oxidation of metal ions at 

In designing layered nanostructures, deposited material forms continuous layers but to achieve the same, deposition must take place in a very controlled manner. Moreover, factors such as temperature, pH of the electrolyte, electrolyte concentration, current density, and deposition time must be kept in mind as they greatly affect the quality of the material deposited. 

Eiectrodeposition runs parallel with the process of electrolysis. Redox reactions taking place in the bath solution simultaneously result in the metal deposition on the cathode, also known as the working electrode. Various steps involved in the eiectrodeposition include (i] oxidation at anode on the application of external current, (ii] dissolution of metal ions in electrolyte solution, (iii] metal ion transportation from electrolytic solution to the cathode surface, (iv] reduction of ions at the cathode, and (v] continuous metal layer formation on the cathode surface. The amount of metal deposition depends on deposition time and other parameters determined by Faraday s law, described by the following equation  

M molar mass of the substance, z the valency of ions, and the ratio M/z the equivalent weight of the substance. 

FIGURE 13.16 Schematic diagram of the electrodeposition of a negative charged ceramic powder onto the cathode of an electrolyte deposition cell. 

Early work on this deposition process are discussed by Overbeek 

Acrylic resins are used for both anodic and cathodic electrodeposition. A detailed discussion of electrodeposition will not be given here. Consult Oldring et al (VbZ. HI Resins for Surface Coatings published by SITA Technology) for further details. 

Acid functional acrylics neutralised with tertiary amines are used for anodic systems, whilst amine functional acrylics neutrahsed with acid are used for cathodic systems. As a general rule cathodic systems are preferred due to less metal ions leaving the metal, but cathodic systems are normally more expensive. 

Most electrodeposition baths operate at very low solids with 10-15% being typical. This can cause bath instability problems if the neutralising agent is too volatile and evaporates whilst in the bath. Being relatively high capital cost equipment means that quality performance is required from the coating. 

Electrodeposition offers the facility to coat surfaces which are hidden from line of sight application techniques, such as spraying. Radiators are one such example, but electrodeposition can only apply the primer or base coat. Only one coat can be applied and it must be the first. The ability to deposit film in these hidden areas is known as throwing power . The more the coating penetrates these areas, the greater the throwing power of the coating. An overview of the electrodeposition process will now be considered. 

Two of the most widely used methods for preparation of alpha sources on a metal backing for counting or spectroscopyare (1) direct evaporation of an aqueous or organic solution and (2) electrodeposition. Other methods, such as volatilization of the sample in a vacuum, adsorption from an aqueous solution, are not so widely used. However, the method of vacuum flashing from a tungsten filament produces very satisfactory sources and is in routine use in some laboratories. (See for example Procedure 4 in Sect. VUI.) 

This method has the advantage of speed and simplicity and the disadvantage of tending to concentrate any mass present in the solution to produce local thick areas. The 

In general, the method is satisfactory if only total alpha counting is to be done. However, in methods which depend on alpha energy analysis, direct evaporation of even a carrier free solution will not be completely satisfactory. The reason for this failure lies in the above mentioned concentration effect to produce an effectively thick plate. The great advantage of other methods in this regard is that the Pu and impurities in the solution to be plated are spread evenly over the entire area of the plate. 

Tuck describes a method for evaporating organic solutions of alpha-emitting materials by heating only the edge of a circular plate, thus confining the liquid to the center. 

The same principle was used by Westrum to evaporate sulfuric acid solutions. 

In general, aqueous electroplating has minimal effect on substrate properties (apart from hydrogen embrittlement). Coated substrates can also be heat treated to promote interdiffusion, although this may result in concentration of elements at grain boundaries, causing embrittlement. Specific elemental electrodeposition processes and properties are reviewed in Ref 25 some examples are given here. 

Nickel plating is widely used for a corrosion- and wear-resistant finish. Typical applications, with a thin top coat of electrodeposited chromium, are decorative trim for automotive and consumer products and office furniture. Nickel deposits are also used for nondecorative purposes for improved wear resistance, for example, on pistons, cylinder walls, ball studs, and so forth. 

Chromium electroplating is also used as decorative and hard coatings. Colored and tarnish-resistant chromium decorative coatings are produced over a base deposit of copper and/or nickel for applications such as those noted above for nickel. Hard chromium coatings are used for hydraulic pistons and cylinders, piston rings, aircraft engine parts, and plastic molds, where resistance to wear, heat abrasion, and/or corrosion are required. 

Cadmium and zinc electroplating provides galvanic corrosion protection when coated on steel. Deposit thickness can vary between 5 and 25 p,m (0.2 and 1 mil), and typical applications for both coatings are found in Table 10. Cadmium is preferred for the protection of steel in marine environments, whereas zinc is preferred in industrial environments. Cadmium is also preferred for fastening hardware and connectors because its coefficient of friction is less than zinc. Cadmium is toxic and should not be used in parts that will have contact with food. Precautions for minimizing hydrogen embrittlement should be taken because cadmium plating is more susceptible to such embrittlement than any other plated metal. 

Tinplate is another continuous electrolytic plating process that has been used for the past 200 years to make containers for the long-term storage of food (Ref 28). The typical tinplate product consists of five layers an 

In electrodepostion processes metal ions are reduced to metal atoms at the cathode of an electrolysis cell. The shape of the cathode can be adjusted to obtain the precipitated metal in a desired form. 

An interesting example is the fluidized bed electrolysis cell, see figure 11.2. 

A fluidized bed electrolysis cell with copper particles of 0.5 mm is used for removing traces of copper ions from waste water. The minimum fluidization velocity of these particles appears to be 0.03 m/s see eq. (4.45), When the flow rate is not higher than 3 times the minimum fluidization velocity, the fluid bed is still homogeneous, i.e. without bubbles. In the pilot plant tests with a superficial velocity of 0.04 m/s, the Cu-content of the waste water is reduced from 100 ppm to 26 ppm when the bed height is 0.35 m, and from 100 to 7 ppm when the bed height is 0.70 m. 

We wish to design a reactor for the treatment of 100 m of waste water per hour, and its Cu-content should be reduced from 100 to 1 ppm. What will the main dimensions be of the fluid bed reactor  

Mass transfer and axial mixing in non-bubbling fluidized beds have not been treated in this book. Indeed, to my knowledge not many data about these effects have been published in literature. Though these effects may not known quantitatively, all transport phenomena can be expected to be approximately linear processes (at low concentrations). The results about mass transfer, first order surface reaction and axial mixing presented in section 72.2,1 may be expected to apply here. 

Metal nanoparticles can also be deposited directly onto the carbon support by classical electrochemical techniques from a solution containing metal species [136-145]. The nature of the electrolyte and the current-potential program used are crucial parameters which allow us to tune the mean particle size and the size 

CARBON MATERIALS AS SUPPORTS FOR FUEL CELL ELECTROCATALYSTS 

Nickel, chromium and zinc are commonly used as electrodeposits. Chromium, the hardest of these coatings, is applied for abrasion resistance 

Electrolytic metal deposition ( electroplating ) is an empirical art widely in use to cover corrosion-sensitive surfaces with a thin protecting metal layer, e.g. of tin, nickel, zinc, etc. The complete plating process comprises several partial processes such as mass transport, charge transfer, adsorption of adatoms, surface diffusion of adatoms, and finally nucleation and crystal growth. 

Researchers have prepared a CNT/CHT nanocomposite film as a glucose biosensor by 

If the current passed, I, is constant, then Q = It, with t the time in seconds of deposition. Since the electrodeposited silver can be weighed, and the atomic weight of silver is known ( 108 gmol ), F is easily inferred from Faraday s laws of electrolysis. 

In an experimental situation, this integration can be performed numerically using a data analysis program. The quantity (in moles) of material deposited can then be deduced directly from the charge passed, provided n is known, (ii) From the charge passed, we can calculate the mass of Cu deposited  

Since the reduction of Ag+ to Ag is a one-electron process, the charge passed per unit area is found by multiplying by the Faraday constant, so that 

Hence the observed Q = 200 ixC cm is consistent with deposition of an ideal monolayer to within 11%, which is good agreement considering the crude geometric model and experimental error. It is therefore reasonable to assume that a single monolayer is deposited in this peak. 

Thin layers of electrochemically deposited metals and thin polymer layers deposited on electrode surfaces can be conveniently studied by ellipsometry combined with other electrochemical experiments. Electrocrystallization of nickel was studied by Abyaneh, Visscher, and Barendrecht with ellipsometry and simultaneous amperometric measurements. The initial changes in A and ij/ showed nonlinear variations with the deposition time (Fig. 12), which is apparently abnormal, indicating a marked deviation of the optical properties of the deposited film from the bulk metal properties. The observed trend was explained by theoretical calculations using equations of effective medium theory (see Section IV.4 for effective medium theory) for hemispherical growth of the nucleation centers. The observed ellipsometry data clearly demonstrate that in the initial stage of nonuniform deposition the measured parameters, ij/ in particular, can change in a 

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The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

At potentials positive to the bulk metal deposition, a metal monolayer-or in some cases a bilayer-of one metal can be electrodeposited on another metal surface this phenomenon is referred to as underiDotential deposition (upd) in the literature. Many investigations of several different metal adsorbate/substrate systems have been published to date. In general, two different classes of surface stmetures can be classified (a) simple superstmetures with small packing densities and (b) close-packed (bulklike) or even compressed stmetures, which are observed for deposition of the heavy metal ions Tl, Hg and Pb on Ag, Au, Cu or Pt (see, e.g., [63, 64, 65, 66, 62, 68, 69 and 70]). In case (a), the metal adsorbate is very often stabilized by coadsorbed anions typical representatives of this type are Cu/Au (111) (e.g. [44, 45, 21, 22 and 25]) or Cu/Pt(l 11) (e.g. [46, 74, 75, and 26 ]) It has to be mentioned that the two dimensional ordering of the Cu adatoms is significantly affected by the presence of coadsorbed anions, for example, for the upd of Cu on Au(l 11), the onset of underiDotential deposition shifts to more positive potentials from 80"to Br and CE [72]. 

Markovic N M, Gasteiger H A and Ross P N 1995 Copper electrodeposition on Pt(111) in the presence of chloride and (bi)sulphate Rotating ring-Pt(111) disk electrode studies Langmuir 11 4098-108... 

Koinuma M and Uosaki K 1996 Atomic structure of bare p-GaAs(IOO) and electrodeposited Cu on p-GaAs (100) surfaces in H2SO4 solutions An AFM study J. Eiectroanai. Chem. 409 45-50... 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

Other types of reactions can be used to chemically separate an analyte and interferent, including precipitation, electrodeposition, and ion exchange. Two important examples of the application of precipitation are the... 

A gravimetric method in which the signal is the mass of an electrodeposit on the cathode or anode in an electrochemical cell. 

In electrogravimetry the analyte is deposited as a solid film on one electrode in an electrochemical cell. The oxidation of Pb +, and its deposition as Pb02 on a Pt anode is one example of electrogravimetry. Reduction also may be used in electrogravimetry. The electrodeposition of Cu on a Pt cathode, for example, provides a direct analysis for Cu +. 

For a description of electrogravimetry, see the following resource. Tanaka, N. Electrodeposition, In Kolthoff, I. M. Living, P. J., eds. Treatise on Analytical Chemistry, Part I Theory and Practice, Vol. 4. Interscience New York, 1963. 

ALKANOIAMNES - ALKANOLAMINES FROM OLEFIN OXIDES AND AMTONIA] (Vol 2) Electrodeposition experiments... 

Electroforrning, which is used in the production of art objects or jewelry is a combination of electroless plating and electro deposition. A wax mold of the object to be produced is made conductive by electroless gold plating, a thick layer of gold or gold alloy is then electrodeposited and, finally, the wax is removed by melting (134). 

Brinell Tests of Steel Products Comparison Hardness Tester Practice Rockwell Test on Cemented Carbides Rockwell Test for Sintered Materials Knoop Test for Electrodeposited Coatings Webster Hardness Gauge Barcol Test of Aluminum Alloys... 

Toxic substances adsorbed on resins are removed during a regeneration procedure. The resulting spent regeneration solution has a higher concentration of the toxic substance than the stream from which it was removed by the resin. Toxic material in the spent regenerating solution can usually be precipitated, electrodeposited as in an electrolytic ceU, or made insoluble by other acceptable procedures. 

D. E. Bartak, T. D. Schleisman, and E. R. Woolsey, "Electrodeposition and Characteristics of a SUicon—Oxide Coating for Magnesium AUoys," Paper T-91-041, North American Die Casting Association 16th International Die Casting Congress and Exposition, Detroit, Mich., 1991. 

J. W. Dini, Electrodeposition The Materials Science of Coatings and Substrates, Noyes Data Corp., Park Ridge, N.J., 1993. 

W. H. Safranek, The Properties of Electrodeposited Metals and Alloys, 2nd ed., American Electroplaters and Surface Finishers Society, Orlando, Fla.,... 

Wrought and cast nickel anodes and sulfur-activated electrodeposited rounds are used widely for nickel electro deposition onto many base metals. 

Copper is universally used as the metal plating for tape because it can be easily laminated with copper and the various plastic tapes. Copper is readily etched and has excellent electrical and thermal conductivity in both electrodeposited and roUed-annealed form. The tape metal plating is normally gold- or tin-plated to ensure good bondabiUty during inner- and outer-lead bonding operations and to provide better shelf life and corrosion resistance. 

Hardness of the aimealed metals covers a wide range. Rhodium (up to 40%), iridium (up to 30%), and mthenium (up to 10%) are often used to harden platinum and palladium whose intrinsic hardness and tensile strength are too low for many intended appHcations. Many of the properties of rhodium and indium. Group 9 metals, are intermediate between those of Group 8 and Group 10. The mechanical and many other properties of the PGMs depend on the physical form, history, and purity of a particular metal sample. For example, electrodeposited platinum is much harder than wrought metal. 

In this process, uranium metal is electrodeposited at the cathode, while plutonium and other transuranium elements remain in the molten salt as trichlorides. Plutonium is reduced in a second step at a metallic cathode to produce Cd—Pu intermetallics. The refined plutonium and uranium metals can then be refabricated into metallic fuel (137). 

Aqueous Electrodeposition. The theory of electro deposition is well known (see Electroplating). Of the numerous metals used in electro deposition, only 10 have been reduced to large-scale commercial practice. The most commonly plated metals are chromium, nickel, copper, zinc, rhodium, silver, cadmium, tin, and gold, followed by the less frequendy plated metals iron, cesium, platinum, and palladium, and the infrequendy plated metals indium, mthenium, and rhenium. Of these, only platinum, rhodium, iddium, and rhenium are refractory. 

R. Sard, H. Leidheiser, Jr., and E. Ogbum, eds.. Properties of Electrodeposits—TheirMeasurement and Significance, Electrochemical Society, Princeton, N.J. 

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